Bevel drive nasty!

[Hiya9612]

Quick background story before I get down to the nitty gritty. I bought a beautiful immaculate 350 Mk3 from a bike dealer a few months ago. It seems to be a bitza, being an Italian head with a Spanish bottom end. All seemed OK until I checked some chassis nuts and bolts and found many to be barely tight, as were the cylinder head bolts, I also realised the completely clean engine oil (as delivered) was extremely underfilled, by 1 litre or so.....
So I've run the bike while the summer weather lasted, for about 300 miles, sorting out the over-rich carburation as I went.
Now that wet autumn weather is here, I drained the oil and removed the timing side cover to check that the Spanish plastic idler gear had been replaced with an Italian steel one.... which it has..... HOWEVER, I found a whole load of nastiness on the lower bevel drive, detailed photos below.
Although there were a few fine metal filings on the outside of the oil strainer I dredged a strong magnet through the old oil and nothing metallic attached itself, so either the damage happened prior to me obtaining the bike or there are bits of bevel metal still inside...... The engine is very clean inside and out so I suspect it hasn't been run very much since someone, somewhere, worked on it.
So, can people suggest what might have triggered this damage? I see that the lower bevel pinion should be shimmed, has that been badly done, or some other cause?
As for fixing the problem, it looks like the crankcases have to be split to release and replace the pinion, I haven't stripped an engine down like that for many years and don't really want to do that now.... could I get away with replacing just the crankshaft pinion (or will the problem just reoccur)? The bevel pinion appears worn, but possibly not too damaged? I'll probably run some flushing oil through to clear any residual debris, if that's OK on these engines?
Any comments gratefully received.

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[Bevel bob]

You dont have to dismantle the bottom of the motor to replace the lower bevels which were most likely damaged through incorrect meshing or random debris perhaps from the brutal treatment of the nut?. The larger bevel can be removed upwards with a little tap from a drift. Getting the mesh depth and then the clearance right will need a selection of shims ,a micrometer and patience ,but all doable and very satisfying when right. A thorough flush with a pressure sprayer to remove any bits. With the head and barrel off check the tower angular contact bearings and the other bevels. I would also check there is no crank end float as this can load up the bottom bevel gears.

[Duccout]

I remember seeing that bike for sale, it looks nice, but any used bike is a risk as anything could have been done to it it 50 years.

I can't see any broken teeth, so you may be able to keep your bevel gears. I would remove the crankshaft nut (left-hand thread) and check the teeth for damage and while the crankshaft bevel gear is removed, push and pull the end of the crank as hard as you can to check for end float on the crank; if there is any then you will have to strip the engine. It may be that the upper bevel gear has not been shimmed to take out all of the play between the two bearings, allowing the gear to float, but you will not know until you undo the crank nut. You will probably have to remove the head to properly shim the bevel gears anyway.

There are some very experienced Ducati guys on here, so advice is plentiful (probably too much!).

Good luck,

Colin

[IanHood]

As others have said, you can replace the bevels without splitting the crankcase. Buy a good selction of the appropriate shims and be prepared to spend a good couple of hours (or more) playing around to get the mesh just right. And I would replace the both bevels with a good used matched set from a reputable supplier. It may even be that they were unmatched in the first place which is what caused the problem.

Ian

[blethermaskite]

If you take the head off that will leave the top lower bevel unloaded and you should be able to determine if the 'mesh' of the lower bevels is currently tight or loose...I would suggest that loose bevels will chatter and are more likely to break teeth, while tight bevels will whine and wear quite badly quite quickly, as suggested you will need to replace what you have with a good used and matched pair of gears and spend some time shimming them up, I would also carefully inspect the bearings in the upper lower bevel steel housing which may have been damaged......as others have said you will firstly need to insure that the crankshaft is properly shimmed to give zero endfloat otherwise the bottom bevels will end up destroyed again. Good luck with it all.
Cheers,
George

[themoudie]

I bought a beautiful immaculate 350 Mk3 from a bike dealer a few months ago. It seems to be a bitza, being an Italian head with a Spanish bottom end. All seemed OK until I checked some chassis nuts and bolts and found many to be barely tight, as were the cylinder head bolts, I also realised the completely clean engine oil (as delivered) was extremely underfilled, by 1 litre or so.....

Motorcycle sold under false pretenses and unfit for purpose, unless sold as a static display! Caveat emptor!

Here is hoping that I can rebuild my MotoTrans 350 widecase engine, better than MotoTrans, as I too have a crankshaft wending it's merry way!

I too would emphasise "first principle" is the crankshaft without end float, central in the crankcases and freely rotating? If you cannot answer to the affirmative, then you need to be able to, before fitting another pair of matched lower bevel gears. In my mind this involves an engine strip, split the cases, keeping all of the fitted shims in their original positions (You may need to change the shims depending upon what you find!) and check all the bearings for smoothness of operation, before going any further. The amount of fine steel shards reflecting light in that timing chest gives me the screaming abdabs, if you were just to "clean them off"! How many of those are in the main bearing, or have passed into the oil pump for ciculation round the engine?

Looking at the crankshaft nut and lock washer, it appears that an air wrench (rattle gun) may have been used to tighten the nut, to an unknown torque! Is the Woodruff key locating the gear in good condition and sound in it's groove? Also the lock washer appears to have been butchered after the nut was tightened.

If you intend to ride the bike, you don't want it nipping up!

It sounds desparate to be sold a pup, with no recourse and I hope that you are able to resolve the issue.

Good health, Bill

[Hiya9612]

Absolutely Bill! Before spending the money, I did some checking into the bike shop I bought it from, and there are a good number of positive reviews apparently from happy customers. But of course these days, you can never be guaranteed that they're genuine.
Another thing that set alarm bells ringing was that, not only were there different quantities of fork oil in but it was so clean that I could see the oil was a different colour in each leg!
In fairness, I was able to find out that the bike had been sold in it's present condition at auction several months earlier, the bike started and ran nicely when I took delivery, (I only really took the timing cover off to check for a plastic idler gear) so I can't point the figure at the bike shop for the bevel bodging. I can say they didn't do the PDI that they promised.....probably thought I was just going to look at it, not ride it.

Cheers
Phil

[Hiya9612]

Thanks to everyone who's posted a reply. I feel a bit cheeky asking for more help but I guess we've all been there at some time and the forum is a fantastic resource.
Today I removed the pinion gear, I read that the nut should be torqued to 8kg, about 70nm (on a Spanish motorcycle restorers blog: https://moticosroyo.com/ducati-road-montar-motor (Set your browser to automatically translate from Spanish)) the nut on mine was nowhere near that, and I was not in the least surprised to find there was NO shimming behind the gear, The other gears in the timing case didn't seem have been shimmed properly either.
I also checked the top drive and (to my eyes) it looked good.
There is no play when pushing the vertical drive top to bottom, so I think that's shimmed OK.
I tried push/pulling on the crankshaft checking for float and there was a very slight mechanical sound (of something, I'm guessing an alternator rotor seating against a bearing race) but pretty well no movement, to my Ducati Newbie eyes it looked OK, I accept it wasn't the most scientific method tho'.
I've uploaded some more photos, this time from a proper camera (rather than a mobile phone) and in daylight.

Pinion Gear1.jpg

Pinion Gear2.jpg

Top End1.jpg

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[themoudie]

Aye Phil, apologies if my comment was pointed, but that wasn't the intention to point anything at you; it was to raise awareness that with these engines a whole "can of worms" can be laid bare, if the builder doesn't understand Ducati bevel engines. Especially, with many Japanese and modern engines being relatively "take out the worn, fit the new" due to the precision of the OME engineering. That's not to say that some of the non-OME isn't diabolical! Many engine builders do not do a lot of measuring before fitting!

I tried push/pulling on the crankshaft checking for float and there was a very slight mechanical sound (of something, I'm guessing an alternator rotor seating against a bearing race) but pretty well no movement, to my Ducati Newbie eyes it looked OK, I accept it wasn't the most scientific method tho'.

After having seen what you have already found inside this engine and the fact that you now write of a "very slight mechanical sound", when testing for crankshaft endfloat, this is with a lubricating film over everything and could easily hide lateral crankshaft movement, which is the very movement that you do not want. Whilst, you don't want to place side loads on the inner races of the main bearings, you don't want any lateral movement either. So, no lateral end float, yet free rotation, with no binding and the crankshaft central to the crankcase mouth.

If anybody disagrees with what I have written before, PLEASE SAY SO AND WHY, I know that without careful tutelage back in 1977, when I first had to dismantle the 450 engine, due to the alternator rotor coming loose on the crank and wrecking the taper, I too would have made a right "Horlicks" of the whole dismantle and rebuild process. Even now I still have to hold myself in check and take sage council from others, on this website and closer to home.

I hope that you can rectify these problems Phil and get to enjoy the beastie. Stay safe tonight with Ciaran in your neck of the woods.

Good health, Bill

[Duccout]

Hi Phil,

I agree with everything Bill says. Your lower levels are toast, and you can either buy a new set (I think at around £250 from the Ducati Vintage site in Italy) or find a set of used ones (make sure that they are for a wide case engine, not narrow case). The top bevels look to be in nice condition.

The issue of end-float on the crank is vital - if there is any, then it will damage the bevel gears again, and it is not easy to detect. The sound that you can hear is possibly the primary gear teeth knocking together as you push and pull the crank; try putting the nut back on to give yourself more to get hold of and try again. You may be lucky and someone has simply shimmed the bottom bevels too tightly; they are the hardest to get right, because you cannot feel for tightness like the cylinder head ones, and there is inevitably a tight spot and a loose spot and some people convince themselves that the tight spot will 'wear in', when all it does is strain the bearings and break teeth.

Don't hesitate to ask for opinions here, as I said there are a lot of knowledgeable people here and they love to help (although they might not always agree!)

cheers,

Colin